Rough hot start idle on XPT Stage 1 map
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This is a discussion on Rough hot start idle on XPT Stage 1 map within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; Hi all, I'm having an issue I hope someone here can suggest a fix for. I got an XPT Stage ...

  1. #1
    rom
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    Rough hot start idle on XPT Stage 1 map

    Hi all,

    I'm having an issue I hope someone here can suggest a fix for. I got an XPT Stage 1 map today (for my 2011 WRX) and installed it on the car, along with the required AEM CAI and Walbro 255 pump.

    On cold start, everything seems to be fine. Idle is about 1200-1500 for a while, then it settles down. Always smooth though.

    While driving, everything is fine too. Coming to a stop quickly seems to dip the idle very slightly, but barely noticeable.

    The big issue is on hot restart. If I start the car while the engine is warm, then I have extremely rough idle for about 30 seconds before it settles down. Doing some logging, it appears to coincide with the fuel pump going from 100% to 33% duty cycle. 100% on the Walbro, I'm assuming, is overloading the FPR at idle and causing the engine to run rich and not be able to control its idle.

    It actually threw a temporary misfire code on cylinder 3 during the rough idle, lighting the MIL. I drove the car with misfire logging, and it doesn't misfire even at WOT during normal driving - just that super rough (almost stalling) idle at at startup.

    Looking online I see the is a fairly common issue. Does anyone know if it's possible to fix this in the map (maybe by not going to 100% for the 30 secs on initial hot start)? Otherwise, any other suggestions to fix this (hopefully not an AFPR needed!)

    So far the map has been great on the few runs I've done today, but I really need to solve that rough hot start idle!

    Thanks!

    S.

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  3. #2
    lit fam XJman's Avatar
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    Have you checked for air leaks around the newly installed intake? It's possible that when uninstalling and installing the new intake you could have damaged the turbo inlet, and it's not uncommon for them to tear.

    I personally wouldn't be happy with a tune that caused a missfire problem.

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  4. #3
    rom
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    Quote Originally Posted by XJman View Post
    Have you checked for air leaks around the newly installed intake? It's possible that when uninstalling and installing the new intake you could have damaged the turbo inlet, and it's not uncommon for them to tear.

    I personally wouldn't be happy with a tune that caused a missfire problem.

    Sent from my SAMSUNG-SM-G935A using Tapatalk
    Thanks XJman! I actually completely replaced the box and silicone piping, all the way up to the turbo compressor hard pipe inlet, so should be good there (using this kit, which the tune is designed for: https://www.aemintakes.com/search/pr...?prod=21-478wr).

    I'm 99% sure it's an overpowered FPR that is causing the issue. I've found many people with my exact issue - unfortunately no resolutions though. Since it's essentially a "mechanical issue", and I believe the map is unable to reduce the hot start 100% duty cycle at the beginning, I think there are only a couple of solutions...

    1) If possible, change the hot start initial map to a target idle of about 1100-1500RPM. This will allow the ECU to compensate for the extra fuel being added for the first 30 seconds. Then after the pump goes to 33% duty, reduce idle to normal. This is essentially what the cold start map does, though it does it based on the coolant temperature. I haven't spent any time with Subaru maps though (my first ever Subaru, which I only got a few months ago), so I'm not sure what's possible yet.

    2) Improve the return flow some how. The FPR is supposed to allow enough fuel back to maintain target pressure. Of course, what's happening now is that the FPR can't evacuate the fuel fast enough, causing an increase in fuel pressure in the rail. Not sure if the FPR design is at fault, or something more fundamental (e.g. return piping restrictions).

    Right now it does seem that some people have this issue, and some people don't. I would love to know why there are some people that don't have this issue with a high flow pump. Maybe it's just the ability of the FPR? Maybe the age of the stock FPR? Maybe small differences component tolerances either put you in the problem or no problem camps?

    Ideally I'd love to solve this with a small map change. However, if I have to replace the FPR that is fine too. I'd rather not go adjustable if it's a known OEM FPR age issue or something (then I'd just get another OEM FPR).

    Appreciate any more insights in to this issue!

    Thanks!

    S.

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    lit fam XJman's Avatar
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    If you have an ap, bump the rpm up and see if the problem still exists. When I had my tgv deletes installed on my 2011 I had to bump the idle a bit or it was a little weak.

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  7. #5
    rom
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    Quote Originally Posted by XJman View Post
    If you have an ap, bump the rpm up and see if the problem still exists. When I had my tgv deletes installed on my 2011 I had to bump the idle a bit or it was a little weak.

    Sent from my SAMSUNG-SM-G935A using Tapatalk
    I'm actually using EcuFlash, so I can adjust the map. I'll take a look at it tomorrow - hopefully I can just adjust the initial 30 second hot start idle (while the pump is at 100% duty), since I suspect the initial 30 seconds will need a significant change to idle (i.e. at least 1200rpm, maybe more, which of course I don't want to run all the time).

    Thanks!

    S.

  8. #6
    lit fam XJman's Avatar
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    Good luck, hope you get it ironed out.

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  9. #7
    rom
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    Quote Originally Posted by XJman View Post
    Good luck, hope you get it ironed out.

    Sent from my SAMSUNG-SM-G935A using Tapatalk
    Thanks XJman. I saw someone mention that only Cobb have the hot restart maps defined... I'm hoping that's no longer the case (i.e. hoping XPT have it too). I have asked them too, but will check myself as well.

    Thanks!

    S.

  10. #8
    rom
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    Hi all,

    Anyone else have any ideas? I looked through the available maps and can't see a warm restart map that doesn't permanently set the idle at a much higher number.

    Thanks!

    S.

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